pubs.acs.org/Organometallics Published on Web 10/13/2009 r 2009 American Chemical Society

6352 Organometallics 2009, 28, 6352–6361

DOI: 10.1021/om900731x

Synthesis and Reactivity of Dialkyl Lutetium Complexes Supported by a

Novel Bis(phosphinimine)carbazole Pincer Ligand

Kevin R. D. Johnson and Paul G. Hayes*

Department of Chemistry and Biochemistry, University of Lethbridge, 4401 University Drive, Lethbridge,AB, Canada, T1K 3M4

Received August 20, 2009

The synthesis of a novel bis(phosphinimine) ancillary ligand based on a carbazole framework isdescribed (HLPh, 4a; HLPipp, 4b; Ph=phenyl, Pipp=para-isopropylphenyl). Protonolysis with Lu-(CH2SiMe3)3(THF)2 afforded the corresponding lutetium dialkyl complexes (LuLPh(CH2SiMe3)2, 5a;LuLPipp(CH2SiMe3)2, 5b), which were thermally sensitive and rapidly underwent intramolecularmetalative alkane elimination to generate LuLPh*(CH2SiMe3)(THF), 6a, and LuLPipp*(CH2SiMe3)-(THF), 6b, as highly reactive intermediates. Complexes 6a and 6b further decomposed, cleanlygenerating doubly metalated complexes LuLPh**(THF), 7a, and LuLPipp**(THF), 7b, respectively, asthe thermodynamic products. Kinetic analysis of the decomposition of 5a revealed a first-ordermechanism with activation parameters ΔHq=19.2(1) kcal 3mol-1 and ΔSq=-8.2(2) cal 3K

-13mol-1.

Compounds 4a, 4b, 6b, and 7b were characterized by single-crystal X-ray diffraction studies.

Introduction

Although organometallic chemistry of group 3 and lantha-nide metals has received an increasing amount of attentionover the past two decades, it still lags significantly behind thatof the transitionmetals.1 This is in part due to the highly ionicnature of the lanthanides and reactivity issues such as ligandredistribution and “ate” complex formation.2 Largely thesechallenges can be overcome through the use of appropriatelanthanide precursors that incorporate sufficient steric bulk tosaturate the coordination sphere of the metal3 or, alterna-tively, with ancillary ligands that impose a multidentate

coordination mode.2b,4 Despite this, the lack of adequateancillaries for supporting these metals has drastically limi-ted their applications in organometallic processes such asolefin polymerization,5 catalytic hydroamination,6 andC-H bond activation.7 While the cyclopentadienyl ligandsystem has been extremely influential in the development

*Corresponding author. E-mail: p.hayes@uleth.ca.(1) (a) Hou, Z.;Wakatsuki,Y.Organometallic Complexes of Scandium,

Yttrium, and the Lanthanides. In Science of Synthesis; Imamoto, T., Noyori,R.,Eds.; Thieme: Stuttgart, 2002;Vol.2, pp 849-942. (b)Edelmann, F.T.Coord.Chem. Rev. 2009, 253, 343–409. (c) Edelmann, F. T. Angew. Chem., Int. Ed.Engl. 1995, 34, 2466–2488.(2) (a) Anwander, R.Top. Organomet. Chem. 1999, 2, 1–61. (b) Piers,W.

E.; Emslie, D. J. H. Coord. Chem. Rev. 2002, 233-234, 131–155.(c) Raymond, K. N.; Eigenbrot, C. W., Jr. Acc. Chem. Res. 1980, 13, 276–283. (d) Piers,W. E.; Shapiro, P. J.; Bunel, E. E.; Bercaw, J. E.Synlett 1990, 74–84. (e) Schumann, H.; M€uller, J. J. Organomet. Chem. 1979, 169, C1–C4.(3) (a) Anwander, R.; Herrmann, W. A. Top. Curr. Chem. 1996, 179,

1–32. (b) Masuda, J. D.; Jantunen, K. C.; Scott, B. L.; Kiplinger, J. L.Organometallics 2008, 27, 1299–1304. (c) Masuda, J. D.; Jantunen, K. C.;Scott, B. L.; Kiplinger, J. L.Organometallics 2008, 27, 803–806. (d) Meyer,N.; Roesky, P.W.; Bambirra, S.;Meetsma,A.;Hessen, B.; Saliu, K.; Takats, J.Organometallics 2008, 27, 1501–1505. (e) Yan, K.; Pawlikowski, A. V.;Ebert, C.; Sadow,A.D.Chem.Commun. 2009, 656–658. (f) Emslie, D. J. H.;Piers, W. E.; Parvez, M.; McDonald, R. Organometallics 2002, 21, 4226–4240. (g) Power, P. P. J. Organomet. Chem. 2004, 689, 3904–3919.(4) (a)Mountford, P.; Ward, B. D.ChemCommun. 2003, 1797–1803.

(b) Chomitz, W. A.; Arnold, J. Chem.;Eur. J. 2009, 15, 2020–2030.(c) Hajela, S.; Schaefer, W. P.; Bercaw, J. E. J. Organomet. Chem. 1997,532, 45–53. (d) Shao, P.; Berg, D. J.; Bushnell, G.W. Inorg. Chem. 1994, 33,3452–3458. (e) Lee, L.; Berg, D. J.; Einstein, F. W.; Batchelor, R. J.Organometallics 1997, 16, 1819–1821. (f) Cheng, J.; Saliu, K.; Kiel, G.Y.; Ferguson, M. J.; McDonald, R.; Takats, J.Angew. Chem., Int. Ed. 2008,47, 4910–4913.

(5) (a) Hayes, P. G.; Piers, W. E.; McDonald, R. J. Am. Chem. Soc.2002, 124, 2132–2133. (b) Yu,N.;Nishiura,M.; Li, X.; Xi, Z.; Hou, Z.Chem.Asian J. 2008, 3, 1406–1414. (c)Watson, P. L. J.Am.Chem.Soc. 1982, 104,337–339. (d) Hou, Z.; Luo, Y.; Li, X. J.Organomet. Chem. 2006, 691, 3114–3121. (e) Gromada, J.; Carpentier, J.-F.; Mortreux, A. Coord. Chem. Rev.2004, 248, 397–410. (f) Nakayama, Y.; Yasuda, H. J. Organomet. Chem.2004, 689, 4489–4498. (g) Hou, Z.; Wakatsuki, Y.Coord. Chem. Rev. 2002,231, 1–22. (h) Edelmann, F. T. Top. Curr. Chem. 1996, 179, 247–276. (i)Gibson, V. C.; Spitzmesser, S. K. Chem. Rev. 2003, 103, 283–315.

(6) (a) Hong, S.; Marks, T. J. Acc. Chem. Res. 2004, 37, 673–686.(b) Hultzsch, K. C. Adv. Synth. Catal. 2005, 347, 367–391. (c) Hultzsch,K. C.; Gribkov, D. V.; Hampel, F. J. Organomet. Chem. 2005, 690, 4441–4452. (d) B€urgstein, M. R.; Berberich, H.; Roesky, P. W. Chem.;Eur. J.2001, 7, 3078–3085. (e) Lauterwasser, F.; Hayes, P.G.; Br€ase, S.; Piers,W.E.;Schafer, L. L. Organometallics 2004, 23, 2234–2237. (f) Stanlake, L. J. E.;Schafer, L. L. Organometallics 2009, 28, 3990–3998. (g) Bambirra, S.;Tsurugi, H.; van Leusen, D.; Hessen, B.Dalton Trans. 2006, 1157–1161. (h)Bambirra, S.; Meetsma, A.; Hessen, B. Organometallics 2006, 25, 3454–3462. (i) Gagn�e, M. R.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1992,118, 275–294. (j) M€uller, T. E.; Hultzsch, K. C.; Yus, M.; Foubelo, F.; Tada,M. Chem. Rev. 2008, 108, 3795–3892. (k) Pohlki, F.; Doye, S. Chem. Soc.Rev. 2003, 32, 104–114. (l) M€uller, T. E.; Beller, M. Chem. Rev. 1998, 98,675–703.

(7) (a) Arndtsen, B. A.; Bergman, R. G.; Mobley, T. A.; Petersen, T.H. Acc. Chem. Res. 1995, 28, 154–162. (b) Watson, P. L.; Parshall, G. W.Acc. Chem. Res. 1985, 18, 51–56. (c) Labinger, J. A.; Bercaw, J. E. Nature2002, 417, 507–514. (d) Sadow, A. D.; Tilley, T. D.Angew. Chem., Int. Ed.2003, 42, 803–805. (e) Sadow, A. D.; Tilley, T. D. J. Am. Chem. Soc. 2005,127, 643–656. (f) Scott, J.; Basuli, F.; Fout, A. R.; Huffman, J. C.; Mindiola,D. J. Angew. Chem., Int. Ed. 2008, 47, 8502–8505. (g) Jantunen, K. C.;Scott, B. L.; Gordon, J. C.; Kiplinger, J. L.Organometallics 2007, 26, 2777–2781. (h) Booij, M.; Deelman, B.-J.; Duchateau, R.; Postma, D. S.; Meetsma,A.; Teuben, J. H.Organometallics 1993, 12, 3531–3540. (i) Watson, P. L. J.Am. Chem. Soc. 1983, 105, 6491–6493. (j) Rothwell, I. P.Polyhedron 1985,4, 177–200. (k) Duchateau, R.; van Wee, C. T.; Teuben, J. H. Organome-tallics 1996, 15, 2291–2302.

Article Organometallics, Vol. 28, No. 21, 2009 6353

of organolanthanide chemistry,8 it is limited in the extent towhich it can be electronically or sterically tuned.9 Thus, thedevelopment of more versatile ancillary ligands may provideaccess to metal complexes with unique structure, reactivity,and enhanced catalytic activity. Herein, we report the synth-esis of a novel family of monoanionic carbazole-based pincerligands and their ability to support well-defined monomericorganolutetium complexes.

Results and Discussion

Ligand Synthesis and Characterization. A novel monoa-nionic ligand has been prepared whereby two phosphiniminedonors have been installed at the 1 and 8 positions of a rigid3,6-dimethylcarbazole (dmc) backbone. The presence ofpolar phosphinimine subunits is desirable, as they have beenshown to provide ancillary ligands with enhanced capacityfor electronic donation.10-12 Furthermore, the phosphini-mine functionality allows for a high degree of steric andelectronic tunability through adjustment of R groups at-tached at the phosphorus and nitrogen atoms. In particular,the incorporation of sufficient steric bulk may assist in

blocking Lewis bases such as tetrahydrofuran (THF) frombinding to the metal center. The presence of stericallydemanding groups can also help to reduce the potential fordimerization; however, the degree of incorporated bulkmustbe carefully selected so as to not completely inhibit reactivityat the metal center.

The high-yielding synthesis of the dmc-based ancillary isoutlined in Scheme 1. From 1,8-dibromo-3,6-dimethylcar-bazole,13 N-protection with tert-butoxycarbonyl afforded 1,which was lithiated and allowed to react with chlorodiphe-nylphosphine to generate the corresponding diphosphine 2.Removal of the protecting group was efficiently achievedunder thermal conditions14 (160 �C for 4.5 h), liberatingdeprotected compound 3. The synthesis of the desired proteoligand (HLPh, 4a; HLPipp, 4b; Ph = phenyl; Pipp = para-isopropylphenyl) was completed by reaction of 3 with anappropriate aryl azide under standard Staudinger condi-tions,15 installing the phosphinimine functionality with con-comitant loss of N2. This four-step synthetic pathway ishighly efficient with overall yields of 73% (4a) and 53% (4b).

Single crystals of 4a suitable for anX-ray diffraction studywere readily obtained upon recrystallization from a benzenesolution layered with pentane at ambient temperature. Themolecular structure of 4a is illustrated in Figure 1 as athermal ellipsoid plot. Ligand 4a was designed to chelatemetals in a tridentatemotif withN1,N2, andN3 occupying acommon plane with the aromatic dmc backbone. In the solidstate, N1 indeed lies approximately within the same plane asthe dmc backbone (N1-P1-C1-C12 torsion angle of-11.1(4)�). However, N3 lies significantly out of this planewith an N3-P2-C8-C9 torsion angle of 68.4(4)�. Therotation of the P2-N3 arm out of the plane of the dmcbackbone is likely due to steric interactions between the twoN-phenyl groups on the phosphinimine moiety. It is possiblethat in the solid state N1 lies within the plane of the dmcbackbone due to the hydrogen-bonding interaction thatexists between it and H2C. The distance between the donorand acceptor nitrogen atoms in the N2-H2C 3 3 3N1 inter-action in 4a is 2.789(5) A.

Similar to 4a, single crystals of 4b were obtained from aconcentrated benzene solution layered with pentane. Themolecular structure of 4b, as determined from an X-raydiffraction experiment, is depicted in Figure 2. Analogousto that described for 4a, ligand 4b has one nitrogen donor(N1) lying in the same plane as the dmc backbone and one(N3) out of the plane. The N1-P1-C1-C12 andN3-P2-C8-C9 torsion angles of 7.8(2)� and -70.7(2)�,respectively, correspond well with that observed for 4a. Incomparison to that of 4a, theN3 group in 4b is rotated about2� further out of plane from the aromatic backbone, whilethe N1 group is approximately 2� closer to the plane of thedmc backbone. This small, but statistically relevant differ-ence may be attributed to the presence of the isopropylgroups in the para positions of the N-aryl rings of 4b, whichcreate slightly greater steric repulsion between the N-arylrings. It is notable that only minor differences in the geome-try of 4a and 4b are observed, a fact that correlates well with

(8) (a) Schumann, H.; Meese-Marktscheffel, J. A.; Esser, L. Chem.Rev. 1995, 95, 865–986. (b) Evans, W. J.; Davis, B. L. Chem. Rev. 2002,102, 2119–2136. (c) Evans, W. J. Inorg. Chem. 2007, 46, 3435–3449.(9) Examples of unique reactivity achieved through tuning of the Cp

ligand: (a) Sun, J.; Berg, D. J.; Twamley, B. Organometallics 2008, 27,683–690. (b) Evans, W. J.; Kozimor, S. A.; Ziller, J. W. J. Am. Chem. Soc.2003, 125, 14264–14265. (c) Evans,W. J.; Kozimor, S.A.; Ziller, J.W. Inorg.Chem. 2005, 44, 7960–7969. (d) Beetstra, D. J.; Meetsma, A.; Hessen, B.;Teuben, J. H.Organometallics 2003, 22, 4372–4374. (e) Evans,W. J.; Allen,N. T.; Ziller, J.W. J.Am.Chem. Soc. 2001, 123, 7927–7928. (f) Evans,W. J.;Allen, N. T.; Ziller, J. W. Angew. Chem., Int. Ed. 2002, 41, 359–361. (g)Jaroschik, F.; Nief, F.; Le Goff, X.-F.; Ricard, L.Organometallics 2007, 26,1123–1125. (h) Jaroschik, F.; Nief, F.; Le Goff, X.-F.; Ricard, L. Organo-metallics 2007, 26, 3552–3558. (i) Jaroschik, F.; Momin, A.; Nief, F.; LeGoff, X.-F.; Deacon, G. B.; Junk, P. C. Angew. Chem., Int. Ed. 2009, 48,1117–1121. (j) Meyer, G.Angew. Chem., Int. Ed. 2008, 47, 4962–4964. (k)Deacon, G. B.; Forsyth, C. M.; Jaroschik, F.; Junk, P. C.; Kay, D. L.;Maschmeyer, T.; Masters, A. F.; Wang, J.; Field, L. D. Organometallics2008, 27, 4772–4778. (l) Ruspic, C.; Moss, J. R.; Sch€urmann, M.; Harder, S.Angew. Chem., Int. Ed. 2008, 47, 2121–2126.(10) (a) Aparna, K.; Ferguson, M.; Cavell, R. G. J. Am. Chem. Soc.

2000, 122, 726–727. (b) Cavell, R. G.; Kamalesh Babu, R. P.; Aparna, K. J. J.Organomet. Chem. 2001, 617, 158–169. (c) Gamer, M. T.; Dehnen, S.;Roesky, P. W. Organometallics 2001, 20, 4230–4236. (d) Gamer, M. T.;Roesky, P. W. J. Organomet. Chem. 2002, 647, 123–127. (e) Zulys, A.;Panda, T. K.; Gamer, M. T.; Roesky, P. W. Chem. Commun. 2004, 2584–2585. (f) Panda, T. K.; Zulys, A.; Gamer, M. T.; Roesky, P. W. Organome-tallics 2005, 24, 2197–2202. (g) Panda, T. K.; Zulys, A.; Gamer, M. T.;Roesky, P. W. J. Organomet. Chem. 2005, 690, 5078–5089. (h) Gamer, M.T.; Rast€atter, M.; Roesky, P. W.; Steffens, A.; Glanz, M. Chem.;Eur. J.2005, 11, 3165–3172. (i) Rast€atter, M.; Zulys, A.; Roesky, P. W. Chem.Commun. 2006, 874–876. (j) Rast€atter, M.; Zulys, A.; Roesky, P. W.Chem.;Eur. J. 2007, 13, 3606–3616. (k) Wiecko, M.; Roesky, P. W.;Burlakov, V. V.; Spannenberg, A. Eur. J. Inorg. Chem. 2007, 876–881. (l)Gamer, M. T.; Roesky, P. W.; Palard, I.; Le Hellaye, M.; Guillaume, S. M.Organometallics 2007, 26, 651–657. (m) Wiecko, M.; Roesky, P. W.Organometallics 2009, 28, 1266–1269. (n) Hill, M. S.; Hitchcock, P. B.DaltonTrans. 2003, 4570–4571. (o) Liddle, S. T.;McMaster, J.; Green, J. C.;Arnold, P. L.Chem. Commun. 2008, 1747–1749. (p)Mills, D. P.; Cooper, O.J.; McMaster, J.; Lewis, W.; Liddle, S. T. Dalton Trans. 2009, 4547–4555.(11) (a) Liu, B.; Cui, D.; Ma, J.; Chen, X.; Jing, X. Chem.;Eur. J.

2007, 13, 834–845. (b) Liu, B.; Liu, X.; Cui, D.; Liu, L. Organometallics2009, 28, 1453–1460. (c) Conroy, K. D.; Piers, W. E.; Parvez, M. J.Organomet. Chem. 2008, 693, 834–846.(12) (a) Wheaton, C. A.; Ireland, B. J.; Hayes, P. G.Organometallics

2009, 28, 1282–1285. (b) Zhu, D.; Budzelaar, P. H. M. Organometallics2008, 27, 2699–2705. (c) Welch, G. C.; Piers, W. E.; Parvez, M.; McDonald,R. Organometallics 2004, 23, 1811–1818. (d) Li, Y.; Wang, Z. Organome-tallics 2002, 21, 4641–4647. (e) Al-Benna, S.; Sarsfield, M. J.; Thornton-Pett, M.; Ormsby, D. L.; Maddox, P. J.; Br�es, P.; Bochmann, M. J. Chem.Soc., Dalton Trans. 2000, 4247–4257. (f) Courtenay, S.; Walsh, D.;Hawkeswood, S.; Wei, P.; Das, A. K.; Stephan, D. W. Inorg. Chem. 2007,46, 3623–3631.

(13) Britovsek,G. J. P.; Gibson,V. C.;Hoarau,O.D.; Spitzmesser, S.K.; White, A. J. P.; Williams, D. J. Inorg. Chem. 2003, 42, 3454–3465.

(14) Rawal, V. H.; Cava, M. P. Tetrahedron Lett. 1985, 26, 6141–6142.

(15) (a) Meyer, J.; Staudinger, H.Helv. Chim. Acta 1919, 2, 635–646.(b) Alajarin, M.; Lopez-Leonardo, C. L.; Llamas-Lorente, P. L.; Bautista, D.Synthesis 2000, 14, 2085–2091.

6354 Organometallics, Vol. 28, No. 21, 2009 Johnson and Hayes

the identical reaction rates of ligand metalation observed forcomplexes 5a and 5b (vide infra).

Proteo ligands 4a and 4b are both C2v symmetric on theNMR time scale. Each ligand exhibits a sharp singlet (δ 5.41,4a; δ 11.7, 4b) in its 31P{1H} NMR (CDCl3) spectrum. The1H NMR spectrum of 4a (CDCl3) has a single methyl reso-nance atδ 2.44, a broadNHpeak atδ 11.8, and an expectedlycomplicated aromatic region. Similarly, the 1H NMR spec-trum of 4b (CDCl3) displays a singlet at δ 2.45 correspondingto the symmetric methyls of the dmc backbone and a broadNH signal at δ 11.7. The 1H NMR spectrum of 4b also fea-tures isopropyl resonances at δ 2.74 (sp, CH) and δ 1.17 (d,CH3) in addition to a well-definedAB spin pattern (δ 6.74, d;δ 6.64, d) corresponding to protons on the N-aryl rings.Organolutetium Reactivity. Complexation with lutetium

was readily achieved via the alkane elimination reaction ofLu(CH2SiMe3)3(THF)2 with 4a or 4b (Scheme 2). Whenequimolar quantities of 4 and Lu(CH2SiMe3)3(THF)2 werereacted in cold (-78 �C) toluene-d8, the corresponding dial-kyl metal complexes LuLPh(CH2SiMe3)2, 5a, and LuLPipp-(CH2SiMe3)2, 5b, began to cleanly form as highly thermallysensitive compounds. Upon warming the solution to 0 �C,complete conversion to dialkyl 5 was achieved, as evidencedby consumption of the sparingly soluble proteo ligand andformation of a clear yellow solution. Accordingly, when thereaction was monitored in situ, the generation of 1 equiv oftetramethylsilane was observed by 1H NMR spectroscopy.Due to the thermal sensitivity of dialkyl species 5a and 5b,neither complex could be isolated as a pure solid. Allattempts to do so resulted in samples contaminated withthe thermodynamic decomposition product 7 (vide infra).However, both complexes were quantitatively generated

Scheme 1. Synthesis of (ArNdPPh2)2(dmc) Ancillary Ligand 4

Figure 1. Thermal ellipsoid plot (50%probability) ofHLPh (4a)with hydrogen atoms (except H2A) and solvent molecules ofcrystallization omitted for clarity. Selected bond distances (A)and angles (deg): P1-N1=1.581(4), P2-N3=1.570(4), N1-P1-C1 = 107.2(2), N3-P2-C8 = 106.0(2), C27-N1-P1 =126.7(3), C45-N3-P2 = 131.3(4).

Figure 2. Thermal ellipsoid plot (50% probability) of HLPipp

(4b) with hydrogen atoms (except H2C) and solvent moleculesof crystallization omitted for clarity. Selected bonddistances (A)and angles (deg): P1-N1=1.574(2), P2-N3=1.575(2), N1-P1-C1 = 105.3(1), N3-P2-C8 = 106.8(1), C27-N1-P1 =128.8(2), C48-N3-P2 = 127.0(2).

Scheme 2. Synthesis of Organolutetium Complexes 5a and 5b

Article Organometallics, Vol. 28, No. 21, 2009 6355

in situ at low temperature and used in this form to furtherinvestigate reactivity. Complexes 5a and 5b were fully char-acterized by multinuclear NMR spectroscopy at low tem-peraturewith no sign of decomposition over the course of theexperiments.

The 1H NMR spectra of 5 in toluene-d8 exhibit diagnosticmethyl and methylene resonances upfield of 0 ppm for theprotons of the trimethylsilylmethyl groups (5a, 271.3 K: δ-0.06 (CH3), -0.79 (CH2); 5b, 249.1 K: δ -0.01 (CH3),-0.72 (CH2)). Upon cooling solutions of 5a or 5b below-60 �C the two trimethylsilylmethyl moieties become in-equivalent with splitting of the methylene resonances, in-dicating a reduction in molecular symmetry from C2v to Cs.In the 31P{1H} NMR spectra (toluene-d8), a significantdownfield shift of the phosphinimine resonance is observedupon complexation with lutetium (5a, 271.3 K: δ 29.6; 5b,249.1 K: δ 29.4). As the phosphinimine functionality ishighly sensitive to its coordination environment, the largedownfield shift is indicative of complexation with the elec-tropositive lutetium center.10-12 In addition, the sharp singleresonance in the 31P{1H} NMR spectrum corroborates thatthe ancillary is bound to lutetium in a κ3-coordinationmode.Although 2 equiv of THF are present in the in situ-generatedreaction mixture, it appears that the dialkyl lutetium com-plex is five-coordinate with no THF donors bound to themetal. Specifically, toluene-d8 solutions of 5 at temperaturesbetween -40 and 0 �C (the range in which 5 is relativelythermally stable) exhibit resonances in the 1H and 13C{1H}NMR spectra consistent with free THF.

At temperatures above 0 �C, toluene solutions of 5 under-go two sequential intramolecular metalative alkane elimina-tions whereby both alkyl groups are liberated asRH through

a σ-bond metathesis pathway with the ortho C-H bonds ofthe adjacent P-phenyl rings. Upon monitoring the decom-position of 5 by 1H and 31P{1H} NMR spectroscopy, theformation of an asymmetric intermediate with C1 symmetrywas observed (Scheme 3). This transient species, assigned asmonometalated complex 6, then undergoes a second intra-molecular σ-bond metathesis process with a phenyl groupfrom the other phosphinimine phosphorus (vide infra), re-leasing a second equivalent of tetramethylsilane. The finalC2

symmetric products 7a and 7b are the result of a rare double-metalation process. These κ

5-bound lutetium diaryl speciesconsist of two six-membered metallacycles complete withbridging phenyl rings.

The loss of symmetry in the final thermodynamic pro-ducts, 7a and 7b, compared to the initial dialkyl complexes(5a and 5b), was difficult to ascertain through 1H NMRspectroscopy due to overlapping signals in the aromaticregion of the spectrum. However, 13C{1H} NMR spectros-copy proved to be diagnostic in this regard. The metalatedipso carbon attached directly to lutetium is highly deshieldedand resonates far downfield as a doublet of doublets at δ204.6 (dd, 2JPC = 41.2 Hz, 4JPC = 1.1 Hz, 7a) and δ 204.7(2JPC=40.9Hz, 4JPC=1.2Hz, 7b). Such values correspondwell with the shifts reported for other neutral lutetium arylspecies such as LuPh3(THF)2 (δ 198.7, benzene-d6),

16 Lu(p-tol)3(THF)2 (δ 195.2, benzene-d6),

16 Lu(C6H4-p-Et)3(THF)2(δ 194.2, benzene-d6),

16 (Cp*)2LuPh (δ 198.5, cyclohexane-d12),

17 and Lu(o-C6H4CH2NMe2)3 (δ 196.7, benzene-d6).18

Figure 3. Stacked plot of 31P{1H} NMR spectra (toluene-d8) depicting the decomposition of 5a to 7a (via intermediate 6a) at 293.5 Kfrom t = 1760 s to t = 15 500 s.

Scheme 3. Intramolecular Decomposition of Dialkyl Complex 5 to Doubly Metalated Complex 7

(16) Zeimentz, P.M.;Okuda, J.Organometallics 2007, 26, 6388–6396.(17) Watson, P. L. J. Chem. Soc., Chem. Commun. 1983, 276–277.(18) Wayda, A. L.; Atwood, J. L.; Hunter, W. E. Organometallics

1984, 3, 939–941.

6356 Organometallics, Vol. 28, No. 21, 2009 Johnson and Hayes

Kinetic Analysis. The decomposition from derivative 5a to6a was quantitatively monitored by 31P{1H} NMR spectro-scopy and revealed to be first order in the dialkyl species. Thereaction progress at 293.5K (from t=1760 s to t=15500 s)is depicted in Figure 3 as a stacked plot of 31P{1H} NMRspectra. As can be seen from the plot, the decreasing con-centration of 5a (δ 29.4) is accompanied by the growth of twobroad peaks resonating at δ 27.5 and 22.7 for asymmetricintermediate 6a. Within 4 h at this temperature complex 6a

gradually converts exclusively to thermodynamic product 7a(δ 25.6).

The reaction was followed over a broad range of tempera-tures (282.4 to 326.9 K; Figure 4a), with observed t1/2 valuesranging from 5690 to 44.7 s (Table 1). Construction ofan Eyring plot (Figure 4b) allowed for extraction of the

Figure 4. (a) First-order plots of the metalation of 5a at varioustemperatures. (b) Eyring plot for the metalation of 5a.

Table 1. Observed Rate Constants for the Intramolecular Meta-

lation of Compounds 5a and 5b to 6a and 6b at Temperatures

Ranging from 282.4 to 326.9 K

compound T/K kobs/s-1 t1/2/s

5a 282.4 1.22� 10-4 56905a 293.5 4.37� 10-4 15905a 295.7 5.89� 10-4 11805a 304.6 1.71� 10-3 4055a 315.7 4.46� 10-3 1555a 326.9 1.55� 10-2 44.75b 295.7 5.98� 10-4 1160

Figure 5. Thermal ellipsoid plot (50% probability) of LuLPipp*-(CH2SiMe3)(THF) (6b) with hydrogen atoms omitted for clarity.

Figure 6. (a) Thermal ellipsoid plot (50% probability) ofLuLPipp**(THF) (7b) with hydrogen atoms and solvent moleculesof crystallization omitted for clarity. Selected bond distances (A)and angles (deg): Lu1-N1=2.293(6), Lu1-N3=2.285(6), Lu1-N2=2.343(6), Lu1-C26=2.472(8), Lu1-C47=2.431(8), Lu1-O1=2.30(1), P1-N1=1.619(6), P2-N3=1.607(7), N1-Lu1-N3=166.3(2), C26-Lu1-C47=176.4(3),N2-Lu1-O1=174.6(4).(b) Thermal ellipsoid plot (50% probability) of LuLPipp**(THF)(7b0) with hydrogen atoms and solvent molecules of crystallizationomitted for clarity. Selected bond distances (A) and angles (deg):Lu1A-N1A=2.291(6), Lu1A-N3A=2.298(6), Lu1A-N2A=2.349(6), Lu1A-C26A=2.450(8), Lu1A-C47A=2.425(8), Lu1A-O1A= 2.35(2), P1A-N1A= 1.606(6), P2A-N3A= 1.612(6),N1A-Lu1A-N3A=167.3(2), C26A-Lu1A-C47A=178.1(2),N2A-Lu1A-O1A= 174.2(6).

Article Organometallics, Vol. 28, No. 21, 2009 6357

activation parameters, ΔHq = 19.2(2) kcal 3mol-1 andΔSq= -8.2(2) cal 3K

-13mol-1, for the metalation process.

These values correspond to that expected for a highlyordered four-centered transition state16,19 and agree wellwith others reported for intramolecular σ-bond metathesisreactions.20

Kinetic data for the conversion of 6a to 7a was notascertained due to problems in accurately determining theconcentration of 6a over the course of decomposition. Suchdifficulty stemmed from the broad peaks for 6a in the 31P-{1H} NMR spectra, which could not be reproducibly inte-grated due to the low signal-to-noise ratio. In addition,certain temperature ranges gave rise to an overlap of reso-nances for 6a and 7a. As such, the sum of the concentrationof 6a and 7a could be readily determined at those tempera-tures; however, it was not always possible to establish theconcentration of each individual species without introducingsignificant error.

At 295.7 K, metalation of 5a proceeds at a rate of 5.89 �10-4 s-1, while that for 5b was found to be 5.98 � 10-4 s-1

(Table 1). The high degree of correlation between these tworates suggests that the presence of the isopropyl groups in thepara positions of theN-aryl rings of 5b does not significantlyalter reactivity. This result was anticipated, as the incor-poration of isopropyl groups on 5b was intended solely forthe purposes of (a) increasing solubility, (b) increasingcrystallinity, and (c) providing more diagnostic 1H NMR

resonances for theN-aryl ring compared to that available for5a. Furthermore, the solid state structures of proteo ligands,4a and 4b, which were used to prepare 5a and 5b, wereessentially isostructural (vide supra).Solid State Structures. In order to unambiguously estab-

lish that the C-H bond activation of the ancillary ligandoccurred through the ortho carbon of the phenyl rings onphosphorus, single-crystal X-ray diffraction studies wereperformed. Crystals of 6b were serendipitously obtainedfrom an in situ-generated solution of 5b in a 4:1 mixture oftoluene and THF at -35 �C over the course of ∼1 week. As5b slowly decomposed at this temperature, intermediate 6bselectively crystallized out of solution. Under these dynamicand highly variable conditions the single crystallinity of 6bwas of low quality, and repeated attempts to grow higherquality crystals of this unstable intermediate were unsuccess-ful. Despite the challenges encountered with crystal quality,a reliable set of low-intensity single-crystal datawas obtainedfor complex 6b. Such data were sufficient for unambiguouslyestablishing the connectivity of the structure; however, nomeaningful comments on the metrical parameters can bemade at this time.

A thermal ellipsoid plot of 6b is depicted in Figure 5. Thesolid state structure confirms that the ligand is bound tolutetium in a κ

4-fashion, binding through three nitrogenatoms, as well as via an ortho carbon of one P-phenyl ring.One trimethylsilylmethyl group remains attached to lutetiumas well as one THF donor, giving rise to a structure withdistorted octahedral geometry. This structural informationcorroborates the postulated intermediate in the conversionof dialkyl complex 5b to diaryl species 7b (Scheme 3). Due tothe very small (<10 mg) crop of crystals obtained from thecrystallization of 6b, insufficient material was available forfurther characterization.

Table 2. Summary of Crystallography Data Collection and Structure Refinement for Compounds 4a, 4b, 6b, and 7b

4aa

4bb

6b 7bc

formula C56H47N3P2 C68H65N3P2 C64H70LuN3OP2Si C138H134Lu2N6O2P4

fw/g 3mol-1 823.91 986.17 1162.23 2382.33cryst syst triclinic triclinic monoclinic monoclinicspace group P1 P1 P21/n P21/na/A 9.018(3) 8.9413(6) 10.7680(13) 10.9319(9)b/A 14.813(4) 16.6229(12) 21.278(3) 44.979(4)c/A 19.162(6) 19.4273(14) 26.917(3) 24.495(2)R/deg 103.236(4) 77.5770(10) 90 90β/deg 99.522(4) 80.3780(10) 99.461(2) 99.5860(10)γ/deg 106.150(4) 78.8940(10) 90 90volume/A3 2320.5(12) 2743.2(3) 6083.3(13) 11876.1(17)Z 2 2 4 4Dcalc/mg 3m

-3 1.179 1.194 1.269 1.332μ/mm-1 0.134 0.124 1.736 1.761F000 868 1048 2392 4888cryst size /mm 0.24 � 0.13 � 0.082 0.25 � 0.14 � 0.055 0.19 � 0.17 � 0.072 0.38 � 0.078 � 0.035cryst color colorless pale green yellow-green green-yellowcryst habit plate plate block needleθ range/deg 1.59-26.37 1.82-25.03 2.14-20.82 1.69-26.37N 31 432 33 540 68 237 158 092Nind 9473 9677 6349 24 286completeness to θ = 27.10� 99.7% 99.8% 99.7% 99.9%Tmax; Tmin 0.7456; 0.6744 0.7456; 0.6894 0.7456; 0.6019 0.7456; 0.6455data/restraints/params 9473/0/553 9677/2/664 6349/4/318 24 286/7/1299GoF on F2 0.809 1.033 1.060 1.111R1

d (I > 2σ(I)) 0.0763 0.0518 0.0994 0.0790wR2

e (I > 2σ(I)) 0.1221 0.1232 0.2487 0.1395ΔFmax and ΔFmin/e 3 A

-3 0.259; -0.260 0.470; -0.411 5.600; -2.051 2.559; -2.021

aCrystallized with onemolecule of benzene in the asymmetric unit. bCrystallized with twomolecules of benzene in the asymmetric unit. cCrystallizedwith two independentmolecules of 7b, threemolecules of benzene, and one disorderedmolecule of pentane in the asymmetric unit; d R1=

P

)Fo|- |Fc )/P|Fo|.

e wR2 = {P

[w(Fo2 - Fc

2)2]/P

[w(Fo2)2]1/2.

(19) Thompson, M. E.; Baxter, S. M.; Bulls, A. R.; Burger, B. J.;Nolan, M. C.; Santarsiero, B. D.; Schaefer, W. P.; Bercaw, J. E. J. Am.Chem. Soc. 1987, 109, 203–219.(20) (a) Hayes, P. G.; Piers, W. E.; Parvez, M.Organometallics 2005,

24, 1173–1183. (b) Conroy, K. D.; Hayes, P. G.; Piers, W. E.; Parvez, M.Organometallics 2007, 26, 4464–4470. (c) Hayes, P. G.; Piers,W. E.; Lee, L.W. M.; Knight, L. K.; Parvez, M.; Elsegood, M. R. J.; Clegg, W. Organo-metallics 2001, 20, 2533–2544.

6358 Organometallics, Vol. 28, No. 21, 2009 Johnson and Hayes

In contrast to the unstable nature of 6b, diaryl lutetium 7b

can easily be prepared on a multigram scale. Reaction of 4bwith Lu(CH2SiMe3)3(THF)2 in benzene for 18 h at ambienttemperature generated 7b, which was isolated as a pureyellow crystalline solid. Recrystallization from a benzenesolution layered with pentane at ambient temperature af-forded large needles of 7b, which were suitable for X-raydiffraction. It was found that complex 7b crystallized withtwo independent molecules in the asymmetric unit, in addi-tion to a variety of solvent molecules. These independentstructures, 7b and 7b0, are enantiomers of one another andare depicted as thermal ellipsoid plots in Figure 6a and b,respectively.

At ∼1.61 A, complexes 7b and 7b0 exhibit P-N bondsthat are elongated relative to that of the free ligand (averageP-N=1.575 A). Such lengthening is indicative of strongdonation from the phosphinimine functionality to the metalcenter; however, such a distance is still consistent with aformal phosphorus-nitrogen double bond.11c The Lu-Caryl

contacts in 7b and 7b0 range from2.425(8) A in 7b0 to 2.472(8)A in 7b. These values fall within the normal range for neutralLu-Caryl bonds.

11a,b,18,21 Complexes 7b and 7b0 both exhibitdistorted octahedral geometry at the lutetium center, withthe ancillary ligand occupying five of the six coordinationsites. The sixth site composing the octahedron is occupied bya THF donor. No attempt has yet been made to remove orexchange the coordinated Lewis base. Future work willexplore such processes and investigate the exciting possibilitythat 7b may serve as a low-valent (Lu(I)) synthon (viametalation reversal promoted by reaction with reagents ofthe form H2ER or H2SiR2 (E=N, P; R=sterically bulkygroup)).22

Concluding Remarks

In summary, the synthesis and characterization of aversatile family of pincer ligands, which represent a newplatform for stabilizing low-coordinate, electronically un-saturated organometallic species, have been described. Thesecarbazole-based ligands have been utilized to prepare mon-omeric base-free dialkyl lutetium complexes. Although thesehighly electrophilic complexes are thermally sensitive andundergo a rare double-metalative mechanism with the orthoC-H bonds of the P-phenyl rings, it is likely that minorstructural modifications will yield complexes that are suffi-ciently stable to allow full exploration of their organometal-lic chemistry. As such, we are currently reducing the stericbulk around the peripheral edge of the ligand. It is antici-pated that replacement of the phenyl groups attached tophosphorus with a less bulky moiety will dampen undesiredmetalation pathways.

Experimental Section

General Procedures. All reactions were carried out under anargon atmosphere with the rigorous exclusion of oxygen andwater using standard glovebox (MBraun) or high vacuum linetechniques, unless specified otherwise. The solvents THF, di-ethyl ether, dichloromethane (DCM), pentane, benzene, andtoluene were dried and purified using a solvent purificationsystem (MBraun) and stored in evacuated 500 mL bombs oversodium benzophenone ketyl (THF and ether), CaH2 (DCM), or“titanocene” (pentane, benzene, and toluene). Deuterated sol-vents were dried over sodium benzophenone ketyl (benzene-d6and toluene-d8) or CaH2 (CDCl3), degassed via three free-ze-pump-thaw cycles, distilled under vacuum, and stored inglass bombs under argon. Unless otherwise specified, all sol-vents required for air-sensitive manipulations were introduceddirectly into the reaction flasks by vacuum transfer with con-densation at-78 �C. For air-stable manipulations, the solventsTHF, diethyl ether, DCM, and n-hexane were purchased fromEMDChemicals and usedwithout further purification. Samplesfor NMR spectroscopy were recorded on a 300 MHz BrukerAvance II (Ultrashield) spectrometer (1H 300.138 MHz, 13C-{1H} 75.468 MHz, 31P{1H} 121.495 MHz) and referencedrelative to either SiMe4 through the residual solvent resonance-(s) for 1H and 13C{1H} or external 85%H3PO4 for

31P{1H}. AllNMR spectra were recorded at ambient temperature (295 K)unless specified otherwise. FT-IR spectra were recorded on aBruker ALPHA FT infrared spectrometer with Platinum ATRsampling. Elemental analyses were performed using an Elemen-tar Americas Vario MicroCube instrument. Phenyl azide,23

1,8-dibromo-3,6-dimethylcarbazole,13 and Lu(CH2SiMe3)3-(THF)2

24 were prepared according to literature procedures. Thecompound 4-isopropylphenyl azide was prepared according to amodified literature procedure.25 Chlorodiphenylphosphine waspurchased from Strem Chemicals and used as received. Alldeuterated solvents were purchased from Cambridge IsotopeLaboratories. All other reagents were obtained from AldrichChemicals or Alfa Aesar and used as received.

4-Isopropylphenyl Azide. Aqueous 5 M HCl (125 mL) wasadded dropwise to a clear dark red solution of 4-isopropylani-line (10.0 g, 74.2mmol) in THF (100mL) at 0 �C. The red-brownsolution was stirred for 15 min, following which a solution ofNaNO2 (5.63 g, 81.6mmol) inH2O (65mL)was added dropwiseover 20 min. Urea (0.708 g, 11.8 mmol) was added as a solid toremove excess nitrous acid. A solution of NaN3 (5.65 g, 87.0mmol) in H2O (50 mL) was added very slowly at 0 �C, afterwhich the solution was stirred at this temperature for a further 2h. The product was extracted into Et2O (3 � 100 mL), and theorganic layer was washed with 1�100 mL of 1 M HCl, driedoverMgSO4, and concentrated in vacuo to give a dark red liquid.The product was purified by filtration through a silica column(20 cm), eluting with hexane. The hexane was removed from theeluent by rotational evaporation, leaving PippN3 as a canaryyellow liquid. Yield: 10.4 g (86.7%). 1H NMR (CDCl3): δ 7.21(d, 2H, J = 8.4 Hz, Ar-H), 6.96 (d, 2H, J = 8.4 Hz, Ar-H),2.90 (sp, 1H, J = 6.9 Hz, CH), 1.24 (d, 6H, J = 6.9 Hz, CH3).13C{1H} NMR (CDCl3): δ 145.9, 137.5, 127.9, 119.1 (Ar-Cs),33.7 (CH), 24.2 (CH3). IR (neat): 2960 (m), 2128 (s), 2092 (s),1506 (s), 1292 (s), 828 (s), 756 (m), 728 (m), 619 (m), 539 (s) cm-1.

(21) (a) Rufanov, K. A.; M€uller, B. H.; Spannenberg, A.; Rosenthal,U. New J. Chem. 2006, 30, 29–31. (b) Wayda, A. L.; Rogers, R. D.Organometallics 1985, 4, 1440–1444. (c) Protchenko, A. V.; Almazova,O. G.; Zakharov, L. N.; Fukin, G. K.; Struchkov, Y. T.; Bochkarev, M. N. J.Organomet. Chem. 1997, 536, 457–463. (d) Rabe, G.W.; Zhang-Presse, M.;Riederer, F. A.; Incarvito, C. D.; Golen, J. A.; Rheingold, A. L. ActaCrystallogr., Sect. E: Struct. Rep. Online 2004, 60, m1389–m1390. (e)Hogerheide, M. P.; Grove, D. M.; Boersma, J.; Jastrzebski, J. T. B. H.;Kooijman, H.; Spek, A. L.; vanKoten, G.Chem.;Eur. J. 1995, 1, 343–350.(f) Gao, W.; Cui, D. J. Am. Chem. Soc. 2008, 130, 4984–4991.(22) (a) Roering, A. J.; Maddox, A. F.; Elrod, L. T.; Chan, S. M.;

Ghebreab, M. B.; Donovan, K. L.; Davidson, J. J.; Hughes, R. P.;Shalumova, T.; MacMillan, S. N.; Tanski, J. M.; Waterman, R.Organometallics 2009, 28, 573–581. (b) Mork, B. V.; Tilley, T. D. J. Am.Chem. Soc. 2004, 126, 4375–4385.

(23) Cwiklicki, A.; Rehse, K.Arch. Pharm. Pharm.Med. Chem. 2004,337, 156–163.

(24) (a)Masuda, J. D.; Jantunen,K. C.; Ozerov,O. V.; Noonan,K. J.T.; Gates, D. P.; Scott, B. L.; Kiplinger, J. L. J. Am. Chem. Soc. 2008,130, 2408–2409. (b) Estler, F.; Eickerling, G.; Herdtweck, E.; Anwander, R.Organometallics 2003, 22, 1212–1222. (c) Arndt, S.; Voth, P.; Spaniol, T. P.;Okuda, J. Organometallics 2000, 19, 4690–4700. (d) Schumann, H.;Freckmann, D. M. M.; Dechert, S. Z. Anorg. Allg. Chem. 2002, 628,2422–2426.

(25) Cvrk, T.; Strobel, H. W. Arch. Biochem. Biophys. 1998, 349, 95–104.

Article Organometallics, Vol. 28, No. 21, 2009 6359

The spectroscopic analysis of this compound agrees with pre-viously published data for the fully characterized product.26

1,8-Dibromo-3,6-dimethyl-9-tBOC-carbazole (1).An intimatemixture of 1,8-dibromo-3,6-dimethylcarbazole (0.468 g, 1.33mmol) and dimethylaminopyridine (0.171 g, 1.40 mmol) wasdissolved in 30 mL of dichloromethane to give a clear yellowsolution. An excess of di-tert-butoxycarbonyl (0.479 g, 2.19mmol) was added via syringe at ambient temperature. The clearred reaction mixture was stirred for 18 h, generating a yellowsolution. The reaction was quenched by addition of 50 mL of 1M HCl. The layers were separated, and the acidic layer wasextracted with a further 2 � 50 mL of DCM. The combinedfractions were then washed with 3 � 50 mL of 1 M NaHCO3

followed by 2� 50mLof 3MNaCl. The organic layer was driedover MgSO4 and filtered, and the solvent was removed undervacuum, giving the N-protected product as an off-white solid.Yield: 0.506 g (84.2%). 1H NMR (CDCl3): δ 7.62 (s, 2H,Ar-H), 7.43 (s, 2H, Ar-H), 2.44 (s, 6H, CH3), 1.68 (s, 9H,OC(CH3)3).

13C{1H} NMR (CDCl3): δ 151.5 (CdO), 137.0,133.3, 133.1, 127.5, 119.3, 106.2 (Ar-Cs), 86.5 (OC(CH3)3), 28.1(OC(CH3)3), 20.9 (CH3). IR (neat): 2978 (w), 2922 (w), 2860 (w),1749 (m, ν CdO), 1557 (w), 1478 (m), 1419 (w), 1368 (m), 1309(m), 1230 (m), 1177 (m), 1127 (s), 1064 (m), 836 (s) cm-1. Anal.Calcd (%) for C19H19Br2NO2: C, 50.36; H, 4.23; N, 3.09.Found: C, 49.83; H, 4.17; N, 3.16.1,8-Bis(diphenylphosphino)-3,6-dimethyl-9-tBOC-carbazole

(2). A pentane solution of tBuLi (1.40 mL, 2.38 mmol) wasadded dropwise to a solution of 1 (0.506 g, 1.12 mmol) in 50 mLof ether at -78 �C, resulting in a cloudy white suspension. Thereaction mixture was stirred at -78 �C for 3.5 h, after which analiquot of chlorodiphenylphosphine (0.425 mL, 2.37 mmol) wasslowly added at -78 �C, producing a red-orange color. Thesolution was allowed to slowly warm to ambient temperature asit was stirred for 16 h, generating a cloudy yellow suspension.The reaction mixture was filtered through a fine-porosity frit toremove insoluble byproducts, and the frit was then washed withether (2� 20 mL) until the washings were colorless. The solventwas removed from the filtrate under reduced pressure to yield agold-colored solid. Recrystallization from a toluene solutionlayered with pentane at -35 �C gave 2 as an off-white solid.Yield: 0.713 g (96.0%). 1H NMR (benzene-d6): δ 7.54 (m, 8H,Ph-H), 7.46 (s, 2H, Ar-H), 7.70 (d, 2H, J = 4.4 Hz, Ar-H),7.06 (ov m, 12H, Ph-H), 2.06 (s, 6H, CH3), 1.40 (s, 9H,OC(CH3)3).

13C{1H} NMR (CDCl3): δ 152.6 (s, CdO), 144.2(d, JCP = 20.9 Hz, Ar-C), 139.0 (d, JCP = 14.8 Hz, Ar-C),135.3 (s, Ar-C), 133.8 (d, JCP = 20.4 Hz, Ar-C), 133.2 (s,Ar-C), 128.3 (s, Ar-C), 128.2 (s, Ar-C), 127.8 (d, JCP = 5.5Hz, Ar-C), 126.2 (d, JCP = 22.2 Hz, Ar-C), 120.5 (s, Ar-C),85.5 (s, OC(CH3)3), 28.2 (t, JCP = 2.6 Hz, OC(CH3)3), 21.3, (s,Ar-CH3).

31P{1H}NMR(benzene-d6): δ-12.0. IR (neat): 3060(w), 2982 (w), 1724 (s, ν CdO), 1557 (w), 1474 (m), 1434 (m),1388 (m), 1398 (m), 1277 (m), 1246 (m), 1139 (s), 1090 (m), 1023(w), 856 (m), 829 (m), 741 (s), 694 (s) cm-1. Anal. Calcd (%) forC43H39NO2P2: C, 77.81; H, 5.92; N, 2.11. Found: C, 78.24; H,6.02; N, 2.39.1,8-Bis(diphenylphosphino)-3,6-dimethyl-9H-carbazole (3).

Toluene (50 mL) was added to a 100 mL bomb charged with 2(9.33 g, 14.1 mmol) to give a cloudy brown suspension. Thebomb was heated to 160 �C for 4.5 h under static vacuum,generating a clear red solution. The product was cannulatransferred to a 100 mL round-bottom flask, where the solventwas removed under vacuum to yield an orange solid. Recrys-tallization from a toluene solution layered with pentane at -35�C gave 3 as an analytically pure pale yellow solid. Yield: 7.43 g(93.8%). 1HNMR (benzene-d6): δ 8.36 (s, 1H, NH), 7.81 (s, 2H,Ar-H) 7.37-7.31 (ovm, 10H,Ar-HþPPh-H), 6.98-6.96 (ovm, 12H, PPh-H), 2.26 (s, 6H, CH3).

13C{1H} NMR (CDCl3): δ

140.8 (d, JCP=12.9Hz,Ar-C), 135.7 (d, JCP=9.7Hz,Ar-C),133.3 (d, JCP=19.1 Hz, Ar-C), 133.2 (d, JCP=16.1 Hz, Ar-C),129.0 (d, JCP = 6.2 Hz, Ar-C), 128.9-128.7 (ov m, 2 Ar-Cs),122.9 (m,Ar-C), 121.8 (Ar-C), 117.0 (d, JCP=12.7Hz,Ar-C),21.5 (CH3).

31P{1H} NMR (benzene-d6): δ -15.4. Anal. Calcd(%) for C38H31NP2: C, 80.98; H, 5.54; N, 2.49. Found: C, 81.19;H, 5.60; N, 2.77.

HLPh (4a). Benzene (150 mL) was added to a flask charged

with 3 (4.73 g, 8.39 mmol) to give a yellow solution. An aliquotof phenyl azide (2.07 g, 17.4 mmol) was added via syringe atambient temperature. Upon addition, a red product rapidlyprecipitated out of solution along with concurrent evolution ofnitrogen gas. The dark red suspension was stirred under anargon atmosphere for 21 h, following which the solvent wasremoved under vacuum and the residue brought into a glove-box. The product was washed with 5 � 2 mL of pentane toremove excess azide and dried thoroughly under reduced pres-sure to afford crude HLPh as a pale red solid. Recrystallizationfrom a hot benzene solution (20 mL) layered with pentane (15mL) at ambient temperature generated 4a as analytically purepale yellow prisms. Yield: 6.03 g (96.4%). 1H NMR (CDCl3): δ11.8 (s, 1H, NH), 8.01 (s, 2H, Ar-H), 7.69 (m, 8H, PPh-H),7.46 (t, 4H, J=6.9Hz, PPh-H), 7.34 (m, 8H, PPh-H), 7.20 (d,2H, J=14.5Hz,Ar-H), 6.85 (t, 4H,NPh-H), 6.68 (d, 4H, J=8.0 Hz, NPh-H), 6.58 (t, 2H, J = 14.5 Hz, NPh-H), 2.44 (s,6H, CH3).

13C{1H} NMR (CDCl3): δ 151.0 (d, JCP = 3.5 Hz,Ar-C), 140.6 (d, JCP= 2.9 Hz, Ar-C), 132.9 (d, JCP= 9.8 Hz,Ar-C), 131.7 (d, JCP=2.6Hz,Ar-C), 131.3 (d, JCP=10.5Hz,Ar-C), 130.8 (d, JCP = 89.5 Hz, Ar-C), 128.7 (d, JCP = 11.8Hz, Ar-C), 128.3 (Ar-C), 128.0 (d, JCP = 12.7 Hz, Ar-C),124.2 (d, JCP=2.5Hz,Ar-C), 123.8 (d, JCP=18.0Hz,Ar-C),123.6 (d, JCP = 8.5 Hz, Ar-C), 117.3 (Ar-C), 111.6 (d, JCP =118.8 Hz, Ar-C), 21.6 (CH3).

31P{1H} NMR (CDCl3): δ 5.4.Anal. Calcd (%) for C50H41NP2: C, 80.52; H, 5.54; N, 5.63.Found: C, 80.60; H, 5.93; N, 5.37.

HLPipp (4b). Benzene (75 mL) was added to a flask charged

with 3 (2.09 g, 3.71 mmol) to give a light yellow solution. Analiquot of 4-isopropylphenyl azide (1.25 g, 7.72 mmol) wasadded via syringe at ambient temperature. Upon addition, thesolution gradually became a red-orange color with concurrentevolution of nitrogen gas. The solution was stirred under anargon atmosphere for 20 h, following which the solvent wasremoved under vacuum and the residue brought into a glove-box. The product was recrystallized from hot benzene (15 mL)layered with pentane (5 mL) at ambient temperature. Pale greencrystals of 4b formed over 24 h and were collected by filtration,washed with 2 � 1 mL of pentane, and dried thoroughly underreduced pressure. Yield: 2.17 g (70.4%). 1H NMR (CDCl3): δ11.7 (s, 1H, NH), 8.00 (s, 2H, Ar-H), 7.71 (m, 8H, PPh-H),7.46 (t, 4H, J=7.4Hz, PPh-H), 7.33 (m, 8H, PPh-H), 7.23 (d,2H, J = 14.6 Hz, Ar-H), 6.74 (d, 4H, J = 8.2 Hz, Pipp-H),6.64 (d, 4H, J = 8.3 Hz, Pipp-H), 2.74 (sp, 2H, J = 6.9 Hz,CH(CH3)2), 2.45 (s, 6H, CH3), 1.17 (d, 12H, J = 6.9 Hz,CH(CH3)2).

13C{1H} NMR (CDCl3): δ 148.3 (Ar-C), 140.5(d, JCP=2.9Hz, Ar-C), 137.5 (Ar-C), 133.0 (d, JCP=9.8Hz,Ar-C), 131.6 (d, JCP=2.5Hz,Ar-C), 131.3 (d, JCP=10.9Hz,Ar-C), 130.9 (d, JCP = 87.2 Hz, Ar-C), 128.6 (d, JCP = 11.7Hz, Ar-C), 127.9 (d, JCP = 12.8 Hz, Ar-C), 126.2 (Ar-C),124.1 (d, JCP=2.6Hz,Ar-C), 123.5 (d, JCP=17.6Hz,Ar-C),123.5 (d, JCP=9.0 Hz, Ar-C), 111.9 (d, JCP=120.2 Hz, Ar-C), 33.2 (CH(CH3)2), 24.4 (CH(CH3)2), 21.6 (CH3).

31P{1H}NMR (CDCl3): δ 4.57. Anal. Calcd (%) for C56H53N3P2: C,81.04; H, 6.44; N, 5.06. Found: C, 80.21; H, 6.50; N, 4.98.

LuLPh(CH2SiMe3)2 (5a).AnNMR tube was charged with 4a

(0.0400 g, 0.0536 mmol) and Lu(CH2SiMe3)3(THF)2 (0.0312 g,0.0537 mmol) and sealed with a rubber septum and parafilm.The tube was cooled to-78 �C, and an aliquot of toluene-d8 (0.5mL) was added via syringe. The tube was removed from the coldbath, shaken briefly to mix the reagents, and then immediatelyinserted into a precooled (271.3 K) NMR probe. The dialkyl

(26) (a) Das, J.; Patil, S. N.; Awasthi, R.; Prasad Narasimhulu, C.;Trehan, S. Synthesis 2005, 11, 1801–1806.

6360 Organometallics, Vol. 28, No. 21, 2009 Johnson and Hayes

complex (5a) was characterized by multinuclear NMR spectro-scopy in situ. No decomposition was observed over the course ofcharacterization (2 h). 1H NMR (toluene-d8, 271.3 K): 8.12 (s,2H, Ar-H), 7.47 (m, 8H PPh-H), 6.93-6.75 (ov m, 24H,Ar-H), 2.29 (s, 6H, CH3), -0.06 (s, 18H, CH3), -0.79 (s, 4H,CH2).

13C{1H} NMR (toluene-d8; 271.3 K): δ 152.5 (d, JCP=3.6 Hz, Ar-C), 147.4 (d, JCP = 7.4 Hz, Ar-C), 137.1 (Ar-C),134.1 (d, JCP = 9.4 Hz, Ar-CH), 132.3 (d, JCP = 2.2 Hz, Ar-CH), 130.9 (d, JCP=11.4 Hz, Ar-CH), 129.4 (d, JCP=7.9 Hz,Ar-CH), 129.1 (d, JCP=2.4 Hz, Ar-CH), 128.6 (d, JCP=11.8Hz, Ar-CH), 127.3 (d, JCP = 9.3 Hz, Ar-C), 126.0 (d,JCP=2.2 Hz, Ar-CH), 125.2 (Ar-C), 123.2 (d, JCP=2.8 Hz,Ar-CH), 108.9 (d, JCP=111.2 Hz, Ar-C), 40.4 (CH2), 21.3(CH3), 4.63 (Si(CH3)3).

31P{1H} NMR (toluene-d8; 271.3 K):δ 29.6.LuLPipp(CH2SiMe3)2 (5b). An NMR tube was charged with

4b (0.0216 g, 0.0260 mmol) and Lu(CH2SiMe3)3(THF)2 (0.0152g, 0.0262 mmol) and sealed with a rubber septum and parafilm.The tube was cooled to-78 �C, and an aliquot of toluene-d8 (0.5mL) was added via syringe. The tube was removed from the coldbath, shaken briefly to mix the reagents, and then immediatelyinserted into a precooled (249.1 K) NMR probe. The dialkylcomplex (5b) was characterized bymultinuclear NMR spectros-copy in situ. No decomposition was observed over the course ofcharacterization (3 h). 1HNMR (toluene-d8; 249.1 K): δ 8.11 (s,2H, Ar-H), 7.49 (m, 8H PPh-H), 7.11-7.10 (ov m, 4H,Ar-H), 6.96-6.79 (ov m, 18 H, Ar-H), 2.63 (sp, 2H, CH-(CH3)2), 2.29 (s, 6H, CH3), 1.13 (d, J = 6.6 Hz, 12H, CH-(CH3)2),-0.01 (s, 18H, Si(CH3)3),-0.72 (s, 4H, CH2).

13C{1H}NMR (toluene-d8; 249.1 K): δ 152.5 (d, JCP = 3.5 Hz, Ar-C),144.8 (d, JCP= 7.5 Hz, Ar-C), 143.4 (d, JCP= 3.6 Hz, Ar-C),137.0 (Ar-C), 134.1 (d, JCP = 9.6 Hz, Ar-CH), 132.2 (Ar-CH), 130.9 (d, JCP=11.6 Hz, Ar-CH), 129.2 (Ar-CH), 128.5(d, JCP=11.7Hz,Ar-CH), 127.3 (d, JCP=9.3Hz,Ar-C), 127.0(Ar-CH), 126.0 (Ar-CH), 125.0 (Ar-C), 108.9 (d, JCP=110.6Hz, Ar-C), 40.0 (CH2), 33.9 (CH(CH3)2), 24.5 (CH(CH3)2),21.3 (CH3), 4.71 (Si(CH3)3).

31P{1H} NMR (toluene-d8; 249.1K): δ 29.4.

LuLPh**(THF) (7a). In a glovebox, a small Erlenmeyer flaskwas chargedwith 4a (0.193 g, 0.259mmol) and Lu(CH2SiMe3)3-(THF)2 (0.147 g, 0.252mmol). Benzene (5mL)was added to thissolid mixture at ambient temperature to give a clear dark redsolution. The reaction mixture was stirred for 18 h, followingwhich the volatiles were removed to afford a yellow powder. Theproduct was recrystallized from a 9:1 benzene/THF solution (10mL) layered with pentane (10 mL). The crystals were collectedby filtration, washed with pentane (2 mL), and dried undervacuum. Yield: 0.201 g (80.5%). 1H NMR (benzene-d6): δ 8.08(s, 2H, Ar-H), 7.97 (m, 4H, PPh-H), 7.71 (m, 2H, PPh-H),7.56 (d, 2H, J=13.4 Hz, Ar-H), 7.11- 6.97 (ov m, 12H, PPh-H), 6.77 (ovm, 10H, NPh-H), 4.00 (s, 4H, OCH2CH2), 2.34 (s,6H,CH3), 1.15 (s, 4H,OCH2CH2).

13C{1H}NMR(benzene-d6):δ 204.6 (dd, 2JCP = 41.2 Hz, 4JCP=1.1 Hz, Lu-Ar-C), 151.5(d, JCP=5.7Hz, Ar-C), 147.5 (d, JCP=7.3Hz,Ar-C), 140.0 (d,JCP=25.6Hz,Ar-CH), 138.5 (d, JCP=126.7Hz,Ar-C), 134.2(d, JCP=8.5 Hz, Ar-CH), 132.2 (d, JCP = 1.7 Hz, Ar-CH),129.6 (d, JCP=8.7 Hz, Ar-CH), 129.1 (d, JCP=2.1 Hz, Ar-CH), 128.7 (s, Ar-CH), 128.6 (d, JCP=7.2 Hz, Ar-CH), 128.2(Ar-CH), 127.8 (d, JCP=3.7 Hz, Ar-CH), 127.0 (d, JCP=9.8 Hz, Ar-C), 126.3 (d, JCP=81.5 Hz, Ar-C), 124.9 (d, JCP=11.3 Hz, Ar-C), 124.6 (d, JCP=14.7 Hz, Ar-CH), 124.2 (d,JCP=2.3 Hz, Ar-CH), 122.6 (d, JCP = 3.2 Hz, Ar-CH), 115.0(d, JCP=87.0 Hz, Ar-C), 71.3 (OCH2CH2), 25.3 (OCH2CH2),21.5 (CH3).

31P{1H} NMR (benzene-d6): δ 25.9. Anal. Calcd(%) for C54H46LuN3OP2: C, 65.52; H, 4.68; N, 4.24. Found: C,64.47; H, 5.02; N, 3.99.

LuLPipp**(THF) (7b). In a glovebox, a small Erlenmeyer flaskwas chargedwith 4b (0.506 g, 0.609mmol) and Lu(CH2SiMe3)3-(THF)2 (0.354 g, 0.0610 mmol). Benzene (5 mL) was added tothis solidmixture at ambient temperature to give a clear dark red

solution. The reactionmixture was stirred for 18 h, giving a darkred solution and a small quantity of an orange solid. An aliquotof THF (0.5 mL) was added to redissolve all material, and theclear red solutionwas then layeredwith pentane (10mL) and leftat ambient temperature to crystallize. Fine needles developedover 48 h, which were collected by filtration, washed withpentane (2 mL), and dried under vacuum. Yield: 0.252 g(38.5%). 1H NMR (benzene-d6): δ 8.14 (s, 2H, Ar-H), 8.00(m, 4H, PPh-H), 7.72 (m, 2H, PPh-H), 7.57 (d, 2H, J=13.4Hz, Ar-H), 7.13- 6.98 (ov m, 12H, PPh-H), 6.69 (dd, 4H, J=8.4, J=2.2Hz, Pipp-H), 6.60 (d, 4H, J=8.2Hz, Pipp-H), 4.04(s, 4H, OCH2CH2), 2.63 (sp, 2H, J = 6.8 Hz, CH(CH3)2), 2.37(s, 6H, CH3), 1.20 (s, 4H, OCH2CH2), 1.14 (d, 6H, J= 6.9 Hz,CH(CH3)(CH3)

0), 1.12 (d, 6H, J = 6.9 Hz, CH(CH3)(CH3)0).

13C{1H}NMR(benzene-d6): δ 204.7 (dd,2JCP=40.9Hz, 4JCP=

1.2 Hz, Lu-Ar-C), 151.6 (d, JCP=5.7 Hz, Ar-C), 144.6 (d,JCP = 7.3 Hz, Ar-C), 142.8 (d, JCP=3.5 Hz, Ar-C), 140.0 (d,JCP=25.3Hz,Ar-CH), 138.5 (d, JCP=127.3Hz,Ar-C), 134.2(d, JCP=8.5 Hz, Ar-CH), 132.0 (d, JCP=2.2 Hz, Ar-CH),129.7 (d, JCP=8.6 Hz, Ar-CH), 128.8 (d, JCP=24.7 Hz, Ar-CH), 128.3 (d, JCP=4.8Hz, Ar-CH), 128.1 (Ar-CH), 127.6 (d,JCP=3.9 Hz, Ar-CH), 127.1 (d, JCP=2.5 Hz, Ar-CH), 126.9(d, JCP=0.96 Hz, Ar-C), 126.7 (d, JCP=81.3 Hz, Ar-C), 124.9(d, JCP=11.3 Hz, Ar-C), 124.5 (d, JCP=14.8 Hz, Ar-CH),124.1 (d, JCP=2.0Hz,Ar-CH), 115.4 (d, JCP=86.2Hz,Ar-C),71.2 (OCH2CH2), 33.9 (CH(CH3)2), 25.4 (OCH2CH2), 24.5(CH(CH3)(CH3)

0), 24.5 (CH(CH3)(CH3)0), 21.5 (CH3).

31P{1H}NMR (benzene-d6): δ 25.0. Anal. Calcd (%) for C60H58Lu-N3OP2: C, 67.10; H, 5.44; N, 3.91. Found: C, 67.07; H, 6.02;N, 3.64.

NMR Kinetics. All rate constants were determined by mon-itoring the 31P{1H} NMR resonance(s) over the course of thereaction (to at least 3 half-lives) at a given temperature. In atypical experiment, proteo ligand 4a (0.0400 g, 0.0536mmol) andLu(CH2SiMe3)3(THF)2 (0.0312 g, 0.0537mmol) were added to aWilmadNMR tube, which was then sealed with a rubber septum(Sigma-Aldrich) and parafilm. The tube was cooled to -78 �Cand 0.5 mL of toluene-d8 was injected via syringe. The tube wasremoved from the cold bath and shaken briefly, generatingLuLPh(CH2SiMe3)2, 5a, in situ. The tube was then immediatelyinserted into the NMR probe, which was pre-equilibrated to theappropriate temperature. The sample was allowed to equilibrateat the set temperature over the course of shimming the tube in themagnet. 31P{1H}NMRspectra (16 scans) were recorded at presettime intervals until the reaction had progressed to at least 3 half-lives. The extent of reaction at each time interval was determinedby integration of the peak intensity of the starting materialrelative to that of the intermediate andproduct.Anappropriatelylong delay between scans was utilized to ensure that integrationwas quantitative and not affected by theT1 relaxation times of thereacting species. A summary of the observed rate constants andhalf-lives is listed in Table 1.

X-ray Crystallography. Suitable crystals of 4a, 4b, 6b, or 7bwere selected, coated in dry Paratone oil, andmounted on a glassfiber. Data were collected at 173 K using a Bruker SMARTAPEX II instrument (Mo KR radiation, λ= 0.71073 A) equip-ped with a CCD area detector and a KRYO-FLEX liquidnitrogen vapor cooling device. Unit cell parameters were deter-mined and refined on all observed reflections using APEX2software.27 Data reduction and correction for Lorentz polariza-tion were performed using the SAINT-Plus software.28 Absorp-tion corrections were applied using SADABS.29 The structurewas solved by Patterson (4a) or direct (4b, 6b, and 7b) methodsand refined by the least-squares method on F2 using the

(27) APEX2, version 2.1-4; DataCollection andRefinement Program;Bruker AXS: Madison, WI, 2006.

(28) SAINT-Plus, version 7.23a; Data Reduction and CorrectionProgram; Bruker AXS: Madison, WI, 2004.

(29) Sheldrick, G. M. SADABS, version 2004/1; Program for Em-pirical Absorption Correction; Bruker AXS: Madison, WI, 2004.

Article Organometallics, Vol. 28, No. 21, 2009 6361

SHELXTL program package.30 Details of the data collectionand refinement are given in Table 2 and the Supporting In-formation.

Acknowledgment. P.G.H. acknowledges financial sup-port from theNatural Sciences andEngineeringResearchCouncil of Canada for a Discovery Grant, the Canada

Foundation for Innovation for a Leaders OpportunityGrant, and the University of Lethbridge for a start-upfund. The authors also wish to thank Dr. Adrien Cot�e(Xerox Canada) for expert assistance with X-ray crystal-lography and Mr. Craig Wheaton of this department forperforming elemental analyses.

Supporting Information Available: X-ray crystallographicdata in PDF format and CIF files are available free of chargevia the Internet at http://pubs.acs.org.

(30) (a) Sheldrick, G. M. SHELXTL, version 6.14; Structure Deter-minationSoftwareSuite; BrukerAXS:Madison,WI, 2003. (b) Sheldrick, G.M. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, A64, 112–122.